1. Field of the Invention
The present invention relates to an electron-emitting device, and also to an electron source substrate, an electron source, a display panel and an image-forming apparatus, using the electron-emitting device. The present invention also relates to methods of producing these devices and apparatus.
2. Related Background Art
In the art of electron-emitting devices, two types are known, one is a thermionic emission source and the other is a cold-cathode emission source. Cold-cathode emission source types include a field emission type (hereafter referred to as an FE type), metal/insulator/metal type (hereafter referred to as an MIM type), and a surface conduction type electron-emitting device.
Examples of FE types are disclosed for example in "Field Emission" (W. P. Dyke and W. W. Dolan, Advance in Electron Physics. 8, 89(1956)) and "Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones" (C. A. Spindt, J. Appl. Phys., 47, 5248(1976)).
An example of an MIM type has been reported by C. M. Mead (J. Appl. Phys., 32,646 (1961)).
An example of a surface conduction type electron-emitting device has been reported by M. I. Elinson (Radio Eng. Electron Phys., 10 (1965)).
Surface conduction type electron-emitting devices use a phenomenon that electron emission occurs when a current is passed through a thin film with a small area formed on a substrate in a direction parallel to the film surface. Various types of surface conduction electron-emitting devices are known. They include a device using a thin SnO.sub.2 film proposed by Elinson et. al., a device using a thin Au film (G. Dittmer, Thin Solid Films, 9, 317 (1972)), a device using a thin In.sub.2 O.sub.3 /SnO.sub.2 film (M. Hartwell and C. G. Fonstad, IEEE Trans. ED Conf., 519 (1975)), and a device using a thin carbon film (Araki et. al., Vacuum, 26(1), 22 (1983)).
The device proposed by Hartwell is taken here as a representative example of a surface conduction type electron-emitting device, wherein its structure is shown in FIG. 39. In this figure, reference numeral 1 denotes a substrate. Reference numeral 4 denotes an electrically-conductive thin film which is formed of a metal oxide in an H pattern by means of sputtering. The electrically-conductive thin film 4 is subjected to a process called energization forming (hereafter referred to simply as a forming process), which will be described in greater detail later, so that an electron emission region 5 is formed in the electrically-conductive thin film 4. The distance L between electrodes is set to a value in the range from 0.5 mm to 1 mm and the width W' is set to 0.1 mm. The detailed position and shape of the electron emission region 5 are not described in the above reference, and thus FIG. 39 is a rough sketch of the structure.
In conventional surface conduction type electron-emitting devices, before using the devices to emit electrons, the electrically-conductive thin film 4 is subjected to an energization forming process thereby forming an electron emission region 5. In this energization forming, a DC voltage or a voltage which rises at a very slow rate for example 1 V/min is applied across the electrically-conductive thin film 4 so that the electrically-conductive thin film is locally broken, deformed, or changed in quality, thereby forming an electron emission region 5 having a high electric resistance. In the electron emission region 5, cracks are partially formed in the electrically-conductive thin film 4 and electrons are emitted via the cracks or via regions near the cracks. After completion of the forming process, a voltage is applied across the electrically-conductive thin film 4 so that a current flows through the electrically-conductive thin film 4 thereby emitting an electron from the electron emission region 5.
The electron-emitting device of the surface conduction type has a simple structure and thus can be easily produced. Therefore, it is possible to dispose a great number of similar devices over a large area. To take such advantages in practical applications such as an electron beam source, a display device or an image display device, etc., extensive research and development is being done.
The inventors of the present invention have investigated the electron-emitting device of the surface conduction type and have proposed a new method of producing an electron-emitting device in Japanese Patent Application Laid-Open No. 2-56822 (1990). FIG. 38 shows the device disclosed in this patent. In this figure, reference numeral 1 denotes a substrate, reference numerals 2 and 3 denote a device electrode, reference numeral 4 denote an electrically-conductive thin film, and reference numeral 5 denotes an electron emission region. This electron-emitting device can be produced as follows. First, device electrodes 2 and 3 are formed on a substrate 1 using a common technique such as vacuum evaporation and photolithography. Then an electrically conductive material is coated on the substrate by means of for example dispersive coating and then is patterned so as to form an electrically-conductive thin film 4. A forming process is then performed by applying a voltage across the device electrodes 2 and 3 thereby forming an electron emission region 5.
However, in the conventional production method described above, it is based on the semiconductor process and thus it is difficult to form a large number of electron-emitting devices over a large area. Besides, this technique needs a special and expensive production apparatus. Furthermore, the above patterning process requires a plurality of long steps. At present, therefore, high cost is required to form a great number of electron-emitting devices over a large area of a substrate. Thus there is a need for a simplified patterning technique.